2.
The atomic number which is 2 stands for how many protons (also electrons, in an uncharged atom) are in the element's atom.
Helium has only 2 electrons.
8
Helium, as the second element in the periodic table, only possesses two electrons. As such, they only encompass a single level.
Helium has two electrons. You can tell from looking at the periodic table because; each element has the same number of electrons as protons (the number of protons is the atomic number, which increases in number as you move from left to right across the periodic table, starting with one at Hydrogen).
Only the two with the smallest atomic numbers, hydrogen and helium. This corresponds to the fact that the innermost shell of electrons can contain only two electrons.
2.You are in terrible need of a periodic table. It's really not that difficult, and it's well worth learning.
Calcium has 20 electrons
Xenon has 54 electrons.
Each element has a specific number that doesn't change. That number is the atomic number they are given on the periodic table. For example Hydrogen has 1 electron, Helium has 2, Lithium has 3, and so on. The number of electrons in a atom would be determined by what ever element it is.
period 3 elements in the periodic table have 3 electrons in there outher shell hence the name.
Chlorine has 17 electrons. It is displayed as atomic number in periodic table.
Two valence electrons
Just so you know, the periodic table does not give any indication of how many electrons an atom has but 95% of sulfur atoms are neutral and so contain 16 electrons.